The field of the invention is alkylation of arylhydroxides and the present invention is particularly concerned with a process for preparing alkyl phenols from phenol and olefins having 6 to 12 carbon atoms in the liquid phase and in the presence of strongly acid ion exchange resins mounted in a fixed bed.
The state of the art of the alkylation of phenols and ion exchange resins useful therein may be ascertained by reference to the Kirk-Othmer "Encyclopedia of Chemical Technology", Vol. 1 (1963), pages 894-895, under the section entitled "Alkylation of Phenols": Vol. II (1967), pages 871-899, under the section entitled "Ion Exchange", particularly pages 881 and 882 where capacity is disclosed: U.S. Pat. No. 3,422,157 of Kaufman et al which issued Jan. 14, 1969: U.S. Pat. No. 2,865,966 of Abadir; and U.S. Pat. No. 2,732,408 of Foote; the disclosures of which are incorporated herein.
Kirk-Othmer, Vol. 1 discloses at pages 894 - 895 that olefins in the C.sub.8 to C.sub.15 range do not enter into the alkylation of phenol as readily as the lower olefins, and for maximum efficiency a closer control over catalyst and operating conditions is required. The alkylation can be catalyzed by a sulfonic acid resin at 70.degree.-100.degree. C. or by p-toluenesulfonic acid hydrate at 80.degree.-150.degree. C., or by a Superfiltrol clay at 80.degree. C.
U.S. Pat. No. 3,422,157 of Kaufman et al defines in Claim 1 which is incorporated herein, a continuous process for the alkylation of phenols comprising the steps of
(A) MAINTAINING IN A CONTINUOUSLY RECIRCULATING REACTION STREAM, A SOLVENT-FREE LIQUEFIED MIXTURE CONSISTING ESSENTIALLY OF PHENOL AND A LIQUEFIED OLEFIN HAVING FROM 4 TO 12 CARBON ATOMS AND A MELTING POINT OF LESS THAN 150.degree. C., at a temperature between 50.degree. C. and 125.degree. C., and in a molar ratio of from 0.5 to 10 moles of phenol per mole of olefin,
(B) PASSING SAID MIXTURE THROUGH A FIRST REACTION ZONE CONTAINING A STATIONARY MASS OF SUBSTANTIALLY ANHYDROUS CATION EXCHANGING RESIN CONTAINING STRONGLY ACIDIC EXCHANGING GROUPS IN ACID FORM AND HAVING A LARGE SURFACE, THEREBY ALKYLATING ONLY A PORTION OF THE PHENOL WITH AT LEAST A PORTION OF SAID OLEFIN,
(C) AND PASSING THE RESULTING REACTION MIXTURE THROUGH A COOLING ZONE TO REMOVE SUFFICIENT HEAT OF REACTION TO KEEP THE REACTION TEMPERATURE BELOW 150.degree. C.,
(d) continuously feeding to said recirculating stream fresh phenol and olefin reactants in amounts such that the recirculation rate is from 2 to 50 times the reactants feed rate;
(e) continuously withdrawing from said recirculating stream a portion thereof containing the alkylated phenol, said withdrawn portion being substantially equivalent to the volume of the feed, and
(f) passing said withdrawn portion directly to a second reaction zone comprising a stationary mass of substantially anhydrous cation exchanging resin containing strongly acidic exchanging groups in acid form and having a large surface area while maintaining sufficient residence time in said second reaction zone to further react and convert the reaction stream to a higher concentration of the desired alkyl phenol;
(g) distilling the effluent from said second reaction zone to remove unreacted phenol and reaction by-product isomers therefrom;
(h) passing the reaction by-product isomers back to the reaction mass between said first and second reaction zones.
It is known to the prior art to alkylate phenol with olefins in the presence of acids, for instance Lewis acids such as sulfuric acid or boron trifluoride. The use of such catalysts requires for instance corrosion-proof equipment, and furthermore, the products obtained lack both the required purity and the desired quality of color.
Attempts have been undertaken to remedy these drawbacks by using activating clays, for instance montmorillonite, as catalysts as disclosed in U.S. Pat. No. 2,732,408. Mostly these catalysts are used in discontinuous operation in stirred vessels. Because of marked contact abrasion, these products however must be separated by means of centrifuges or filter presses from the elutriated catalyst particles. Furthermore, the dwell times are very long and hence lead to low space time yields. Also, even after separating the elutriated catalysts, there remains a tendency toward undesired colorations during further processing.
Recently, strongly acid ion exchange resins in H-ion form, especially sulfonated ion exchange resins such as sulfonated ion exchange resins based on phenol-formaldehyde resins or polystyrene resins or the same have been used as fixed bed catalysts for alkylating, as disclosed in U.S. Pat. No. 3,422,157, and as sold by Bayer AG as Lewatit (R).sub.s SC 102 H, SC 104H, SC 108H, SPC 108H and SPC 118H. While high space time yields are obtained, local overheating due to the strongly exothermic reaction may not be reliably excluded. This results in contaminated and especially in discolored alkyl phenols which are unsuitable for further use. Also, the ion exchange resins suffer damage.
The process of U.S. Pat. No. 3,422,157 avoids local overheating by circulating the reaction mixture consisting of the alkyl phenols formed from olefins and phenols via a heat exchanger and through the reactor and by only partly alkylating, whereupon the amount corresponding to the fresh supply of olefins and phenols is subtracted and made to react in a second stage. The drawback of this process consists in the expenditure of circulating the reaction components and in their thermal loading, which leads to dissociation or discoloration of the end products.